3.20 Olelo Pa'a' (Promise)

Hawaii Five-0 - Episode 3.20 - 'Olelo Pa'a' (Promise) - Casting News - Alan Ritchson to play Steve's Navy Friend
This is the answer to who was sitting besides McGarrett in yesterday's teaser pics from Peter Lenkov
"Blue Mountain State" star Alan Ritchson spent some time in Hawaii last year, filming scenes for "The Hunger Games: Catching Fire" -- and now he's returning to the Aloha State for some time with Danny and McGarrett.
Ritchson has nabbed a guest-starring role on CBS' "Hawaii Five-0," and Zap2it has your exclusive details. He plays Freddie, described as a sweet guy who is built like a fullback. Freddie is a Navy SEAL -- and he was McGarrett's best buddy during his years in the military.
We'll see them in flashbacks to their time training, when they supported each other through some extremely difficult conditions, and later, in battle together, when they had to make some painful choices together.
Ritchson is best known for his work as Thad Castle on "Blue Mountain State" and as "Smallville's" Aquaman. He'll appear this fall in "Catching Fire" as Gloss, one of the career tributes in the Quarter Quell Hunger Games.
We have also announced that Terry will be returning yesterday and also Jimmy Buffett will be returning as Frank Banna as confirmed over a month ago on his tour stop in the U.S.
Credit: Zap 2 it

Hawaii Five-0 - Episode 3.20 - Olelo Pa’a - Synopsis

WHEN McGARRETT AND CATHERINE CROSS INTO NORTH KOREA TO RETRIEVE THE REMAINS OF A FALLEN FRIEND, HE RECOUNTS HIS LAST DEADLY MISSION THERE, ON “HAWAII FIVE-0,” MONDAY, APRIL 15
The Episode Serves as a Prequel to the Series’ Pilot

“Olelo Pa’a” – When McGarrett and Catherine cross into North Korea to retrieve the remains of a fallen friend, he recounts his last deadly mission there, on HAWAII FIVE-0, Monday, April 15 (10:00-11:00 PM, ET/PT) on the CBS Television Network. The episode serves as a prequel to the series’ pilot. Jimmy Buffett returns as Frank Bama and Terry O’Quinn returns as Joe White.